I found (80 cents) these both
Xenophora conchyliophora on yard sales / flea market
Capdenac-le-haut (Lot) this summer (2010). The saleswoman (gracious)
told me have picked up these ones last year, in scuba diving to south
of Guadeloupe, side Grande-Terre (St Anne, Le Gosier ....). He lives
in the Caribbean on the coast of Florida where it is deemed common in
shallow water but go to see it on dead coral! I almost left in their
box, taking them for eroded corals! Size: 51 and 53 mm.